Power amplifier

ABSTRACT

A power amplifier includes a power splitter that splits a first signal into a second signal and a third signal delayed from the second signal by about 90°, a first amplifier that outputs a fourth signal by amplifying the second signal when a power level of the first signal equals/exceeds a first level, a second amplifier that outputs a fifth signal by amplifying the third signal when the power level of the first signal equals/exceeds a second level higher than the first level, a first phase shifter that receives the fourth signal and outputs a sixth signal delayed from the fourth signal by about 45°, a second phase shifter that receives the fifth signal and outputs a seventh signal advanced from the fifth signal by about 45°, and a combining unit that outputs an amplified signal of the first signal by combining the sixth and seventh signals.

BACKGROUND

1. Field

The present disclosure relates to a power amplifier.

2. Description of the Related Art

As a high-efficiency power amplifier, a Doherty amplifier is disclosed,for example, in Japanese Unexamined Patent Application Publication No.8-330873. As disclosed in the publication, a Doherty amplifier includesa carrier amplifier and a peak amplifier connected in parallel. Thecarrier amplifier operates irrespective of the power level of the inputsignal. The peak amplifier is off when at a low power level of the inputsignal and operates at a high power level of the input signal. In such aDoherty amplifier, a λ/4 transmission line is commonly adopted on theoutput side of the carrier amplifier to change the load impedance of thecarrier amplifier in accordance with the operating state of the peakamplifier.

SUMMARY

As described above, the Doherty amplifier has drawn attention as ahigh-efficiency amplifier. A common Doherty amplifier, however, isunsuitable for being mounted in a small electronic device such as acellular phone due to a large circuit size of the λ/4 transmission line.

The present disclosure has been made in view of the above circumstances,and it provides a power amplifier capable of realizing high efficiencyand a reduction in size.

A power amplifier according to an aspect of the present disclosureincludes a power splitter, a first amplifier, a second amplifier, afirst phase shifter, a second phase shifter, and a combining unit. Thepower splitter splits a first signal into a second signal and a thirdsignal delayed from the second signal by about 90 degrees. The firstamplifier outputs a fourth signal by amplifying the second signal when apower level of the first signal equals or exceeds a first level. Thesecond amplifier outputs a fifth signal by amplifying the third signalwhen the power level of the first signal equals or exceeds a secondlevel higher than the first level. The first phase shifter receives aninput of the fourth signal and outputs a sixth signal delayed from thefourth signal by about 45 degrees. The second phase shifter receives aninput of the fifth signal and outputs a seventh signal advanced from thefifth signal by about 45 degrees. The combining unit outputs anamplified signal of the first signal by combining the sixth signal andthe seventh signal.

According to the present disclosure, a power amplifier capable ofrealizing high efficiency and a reduction in size is provided.

Other features, elements, characteristics, and advantages of the presentdisclosure will become more apparent from the following detaileddescription of embodiments of the present disclosure with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration example of a poweramplifier as an embodiment of the present disclosure;

FIG. 2 is characteristics illustrating an example of operatingcharacteristics of a carrier amplifier and a peak amplifier;

FIG. 3 is a diagram illustrating a state in which the carrier amplifieris on and the peak amplifier is off;

FIG. 4 is a diagram illustrating a state in which the carrier amplifierand the peak amplifier are both on;

FIG. 5 is a diagram illustrating a path on the side of the carrieramplifier in the state of FIG. 4;

FIG. 6 is a diagram illustrating a path on the side of the peakamplifier in the state of FIG. 4;

FIG. 7 is a diagram for illustrating that a parallel circuit formed of agrounded capacitor and a grounded inductor is omissible;

FIG. 8 is a diagram illustrating another example of the configuration ofthe power amplifier;

FIG. 9 is characteristics illustrating an example of simulation resultsof the phase difference between the output of the carrier amplifier andthe output of the peak amplifier;

FIG. 10A is characteristics illustrating an example of a simulationresult of the power added efficiency obtained in a common Dohertyamplifier;

FIG. 10B is characteristics illustrating an example of a simulationresult of the power added efficiency obtained in the power amplifier inFIG. 8; and

FIG. 11 is a diagram illustrating another example of the configurationof the power amplifier.

DESCRIPTION OF THE EMBODIMENTS

With reference to the drawings, an embodiment of the present disclosurewill be described below. FIG. 1 is a diagram illustrating aconfiguration example of a power amplifier as an embodiment of thepresent disclosure. A power amplifier 100 is mounted in a cellularphone, for example, and used to amplify the power of a signal that istransmitted to a base station. The power amplifier 100 includes aninitial-stage amplifier 110, a carrier amplifier 111, a peak amplifier112, matching networks (MNs) 120 and 121, a coupled-line 3 dB coupler(hereinafter simply referred to as “3 dB coupler”) 130, phase shifters140 and 141, a combining unit 142, an inductor 150, and a capacitor 151.The power amplifier 100 may be formed on a single IC chip or multiple ICchips.

The initial-stage amplifier 110 (a third amplifier) amplifies a radiofrequency (RF) signal RF_(IN) (an input signal) input via the matchingnetwork 120, and outputs an amplified signal (a first signal). Thefrequency of the signal RF_(IN) is about a few gigahertz, for example.

The carrier amplifier 111, the peak amplifier 112, the 3 dB coupler 130,the phase shifters 140 and 141, and the combining unit 142 form asecond-stage amplifier circuit which amplifies the signal output fromthe initial-stage amplifier 110 (the first signal), and which is similarin configuration to a common Doherty amplifier.

The 3 dB coupler 130 (a power splitter) splits the signal output fromthe initial-stage amplifier 110 (the first signal) into a signal to thecarrier amplifier 111 (a second signal) and a signal to the peakamplifier 112 (a third signal). The phase of the signal to the peakamplifier 112 is delayed from the phase of the signal to the carrieramplifier 111 by about 90 degrees.

The carrier amplifier 111 (a first amplifier) amplifies the signal inputthereto (the second signal), and outputs an amplified signal (a fourthsignal). Further, the peak amplifier 112 (a second amplifier) amplifiesthe signal input thereto (the third signal), and outputs an amplifiedsignal (a fifth signal).

FIG. 2 is characteristics illustrating an example of operatingcharacteristics of the carrier amplifier 111 and the peak amplifier 112.In FIG. 2, the horizontal axis represents the voltage of the signalRF_(IN), and the vertical axis represents the current flowing throughthe respective amplifiers. Meanwhile, the peak amplifier 112 operateswhen the voltage level of the signal RF_(IN) equals or exceeds a levelV_(BACK), which is lower than a maximum level V_(MAX) by a predeterminedvalue. That is, the peak amplifier 112 operates when the power level ofthe signal RF_(IN) equals or exceeds a level (a second level) lower thana maximum level by a predetermined value (6 dB, for example).

The phase shifter 140 (a first phase shifter) includes an inductor 160(a first inductor) and a capacitor 161 (a second capacitor). Theinductor 160 is connected in series between the carrier amplifier 111and the combining unit 142. The capacitor 161 has one end electricallyconnected to the combining unit 142 and the other end grounded. Thephase shifter 140 outputs a signal (a sixth signal), and the phase ofwhich is delayed from the phase of the signal output from the carrieramplifier 111 (the fourth signal) by about 45 degrees. In the presentembodiment, the inductance of the inductor 160 is set to L=R_(L)/ω.Further, in the present embodiment, the capacitance of the capacitor 161is set to C=1/(2R_(L)ω). Herein, R_(L) represents the impedance from thecombining unit 142 to the matching network 121, and ω represents theangular frequency corresponding to the center frequency of the signalRF_(IN). The principle of phase conversion in the phase shifter 140 willbe described later.

The phase shifter 141 (a second phase shifter) includes a capacitor 170(a first capacitor) and an inductor 171 (a second inductor). Thecapacitor 170 is connected in series between the peak amplifier 112 andthe combining unit 142. The inductor 171 has one end electricallyconnected to the combining unit 142 and the other end grounded. Thephase shifter 141 outputs a signal (a seventh signal), and the phase ofwhich is advanced from the phase of the signal output from the peakamplifier 112 (the fifth signal) by about 45 degrees. In the presentembodiment, the capacitance of the capacitor 170 is set to C=1/(R_(L)ω).Further, in the present embodiment, the inductance of the inductor 171is set to L=2R_(L)/ω. The principle of phase conversion in the phaseshifter 141 will be described later.

The combining unit 142 outputs a combined signal of the signal outputfrom the phase shifter 140 (the sixth signal) and the signal output fromthe phase sifter 141 (the seventh signal) via the matching network 121as an amplified signal RF_(OUT) of the signal RF_(IN).

FIG. 3 is a diagram illustrating a state in which the carrier amplifier111 is on and the peak amplifier 112 is off, that is, the signal RF_(IN)is lower than the level V_(BACK). Since the peak amplifier 112 is off inthis case, the impedance on the output side of the peak amplifier 112 isideally open. As described later, the capacitor 161 and the inductor 171are omissible. When R_(L) represents the impedance on the load side (onthe side of the matching network 121) viewed from the combining unit 142and the capacitor 161 and the inductor 171 are ignored, therefore, theload-side impedance viewed from the output of the inductor 160 is alsoR_(L). Accordingly, the load-side impedance viewed from the output ofthe carrier amplifier 111 is expressed asR_(L)+jω×(R_(L)/ω)=R_(L)+j×R_(L).

FIG. 4 is a diagram illustrating a state in which the carrier amplifier111 and the peak amplifier 112 are both on and an equal current flowstherethrough, that is, the signal RF_(IN) is at the maximum levelV_(MAX). In this case, the peak amplifier 112 is on, and the samecurrent as that in the carrier amplifier 111 flows through the peakamplifier 112. When R_(L) represents the impedance on the load side (onthe side of the matching network 121) viewed from the combining unit142, therefore, the load-side impedance viewed from the output of thephase shifter 140 and the load-side impedance viewed from the output ofthe phase shifter 141 are both 2R_(L) with the power splitting of theload-side impedance R_(L). That is, since the phase shifters 140 and 141are connected in parallel, the combined impedance of the phase shifters140 and 141 needs to be 2R_(L), twice the load-side impedance R_(L), inorder to match the combined impedance and the load-side impedance R_(L).In this state, the phase shifter 140 delays the phase by about 45degrees, and performs impedance conversion between the load-sideimpedance (R_(L)) viewed from the output of the carrier amplifier 111and the load-side impedance (2R_(L)) viewed from the output of the phaseshifter 140. Further, the phase shifter 141 advances the phase by about45 degrees, and performs impedance conversion between the load-sideimpedance (R_(L)) viewed from the output of the peak amplifier 112 andthe load-side impedance (2R_(L)) viewed from the output of the phaseshifter 141. The principle of phase conversion and impedance conversionwill be described below.

FIG. 5 is a diagram illustrating a path on the side of the carrieramplifier 111 in the state of FIG. 4. Herein, V₁ and I₁ respectivelyrepresent the voltage and the current on the input side of the phaseshifter 140, and V₂ and I₂ respectively represent the voltage and thecurrent on the output side of the phase shifter 140. Since the load-sideimpedance viewed from the output of the phase shifter 140 is 2R_(L), thecurrent I₂ is expressed by the following equation.

$\begin{matrix}{I_{2} = \frac{V_{2}}{2\; R_{L}}} & \lbrack {{Math}.\mspace{14mu} 1} \rbrack\end{matrix}$

Further, the current I₁ is expressed by the following equation.

$\begin{matrix}{I_{1} = {{I_{2} + \frac{V_{2}}{\frac{1}{{j\omega}\frac{1}{2\; R_{L}\omega}}}} = {{\frac{V_{2}}{2\; R_{L}}( {1 + j} )} = {( {1 + j} )I_{2}}}}} & \lbrack {{Math}.\mspace{14mu} 2} \rbrack\end{matrix}$

Further, the voltage V₁ is expressed by the following equation.

$\begin{matrix}{V_{1} = {{V_{2} + {I_{1}{j\omega}\frac{R_{L}}{\omega}}} = {{V_{2} + {\frac{j - 1}{2}V_{2}}} = {\frac{1 + j}{2}V_{2}}}}} & \lbrack {{Math}.\mspace{14mu} 3} \rbrack\end{matrix}$

The above equation reveals that the phase of the voltage V₂ is delayedfrom the phase of the voltage V₁ by about 45 degrees.

Further, the load-side impedance viewed from the output of the carrieramplifier 111 is expressed by the following equation.

$\begin{matrix}{\frac{V_{1}}{I_{1}} = {\frac{\frac{1 + j}{2}V_{2}}{( {1 + j} )I_{2}} = {{\frac{1}{2} \cdot \frac{V_{2}}{I_{2}}} = {{{\frac{1}{2} \cdot 2}\; R_{L}} = R_{L}}}}} & \lbrack {{Math}.\mspace{14mu} 4} \rbrack\end{matrix}$

The above equation reveals that the load-side impedance viewed from theoutput of the carrier amplifier 111 is R_(L).

FIG. 6 is a diagram illustrating a path on the side of the peakamplifier 112 in the state of FIG. 4. Herein, V₁ and I₁ respectivelyrepresent the voltage and the current on the input side of the phaseshifter 141, and V₂ and I₂ respectively represent the voltage and thecurrent on the output side of the phase shifter 141. Since the load-sideimpedance viewed from the output of the phase shifter 141 is 2R_(L), thecurrent I₂ is expressed by the following equation.

$\begin{matrix}{I_{2} = \frac{V_{2}}{2\; R_{L}}} & \lbrack {{Math}.\mspace{14mu} 5} \rbrack\end{matrix}$

Further, the current I₁ is expressed by the following equation.

$\begin{matrix}{I_{1} = {{I_{2} + \frac{V_{2}}{{j\omega}\frac{2\; R_{L}}{\omega}}} = {{\frac{V_{2}}{2\; R_{L}}( {1 - j} )} = {( {1 - j} )I_{2}}}}} & \lbrack {{Math}.\mspace{14mu} 6} \rbrack\end{matrix}$

Further, the voltage V₁ is expressed by the following equation.

$\begin{matrix}{V_{1} = {{V_{2} + {I_{1}\frac{1}{{j\omega}\frac{1}{R_{L}\omega}}}} = {{V_{2} - {\frac{j + 1}{2}V_{2}}} = {\frac{1 - j}{2}V_{2}}}}} & \lbrack {{Math}.\mspace{14mu} 7} \rbrack\end{matrix}$

The above equation reveals that the phase of the voltage V₂ is advancedfrom the phase of the voltage V₁ by about 45 degrees.

Further, the load-side impedance viewed from the output of the peakamplifier 112 is expressed by the following equation.

$\begin{matrix}{\frac{V_{1}}{I_{1}} = {\frac{\frac{1 - j}{2}V_{2}}{( {1 - j} )I_{2}} = {{\frac{1}{2} \cdot \frac{V_{2}}{I_{2}}} = {{{\frac{1}{2} \cdot 2}\; R_{L}} = R_{L}}}}} & \lbrack {{Math}.\mspace{14mu} 8} \rbrack\end{matrix}$

The above equation reveals that the load-side impedance viewed from theoutput of the peak amplifier 112 is R_(L).

According to the power amplifier 100 having such a configuration, onlythe carrier amplifier 111 operates when the power level of the signalRF_(IN) is relatively low (lower than a back-off level of about 6 dB,for example). Further, the carrier amplifier 111 and the peak amplifier112 both operate when the power level of the signal RF_(IN) isrelatively high (equal to or higher than a back-off level of about 6 dB,for example). Moreover, in the power amplifier 100, the phase shifters140 and 141 are capable of realizing functions equivalent to those of aλ/4 transmission line of a common Doherty amplifier.

A description will now be given that the capacitor 161 of the phaseshifter 140 and the inductor 171 of the phase shifter 141 are omissible.As illustrated in FIG. 7, it is possible to view the capacitor 161 andthe inductor 171 as a parallel circuit having one end connected to thecombining unit 142 and the other end grounded. A combined impedanceZ_(LC) of the capacitor 161 and the inductor 171 is expressed by thefollowing equation.

$\begin{matrix}\begin{matrix}{Z_{LC} = \frac{{j\omega}\; {L \cdot \frac{1}{{j\omega}\; C}}}{{{j\omega}\; L} + \frac{1}{{j\omega}\; C}}} \\{= \frac{{j\omega}{\frac{2\; R_{L}}{\omega} \cdot \frac{1}{{j\omega}\frac{1}{2\; R_{L}\omega}}}}{{{j\omega}\frac{2\; R_{L}}{\omega}} + \frac{1}{{j\omega}\frac{1}{2\; R_{L}\omega}}}} \\{= \frac{{j2}\; {R_{L} \cdot \frac{2\; R_{L}}{j}}}{{{j2}\; R_{L}} + \frac{2\; R_{L}}{j}}} \\{= \frac{4\; R_{L}^{2}}{2\; {R_{L}( {j - j} )}}} \\{= \infty}\end{matrix} & \lbrack {{Math}.\mspace{14mu} 9} \rbrack\end{matrix}$

As in the above equation, the combined impedance of the capacitor 161and the inductor 171 becomes infinite with the impedance of each of thecapacitor 161 and the inductor 171 set to a predetermined value.Accordingly, the capacitor 161 and the inductor 171 are omissible. FIG.8 is a diagram illustrating a configuration of a power amplifier 100A,which corresponds to the power amplifier 100 illustrated in FIG. 1 withthe capacitor 161 and the inductor 171 omitted therefrom. The sameconfigurations as those of the power amplifier 100 illustrated in FIG. 1are designated by the same reference numerals, and description thereofwill be omitted. As illustrated in FIG. 8, the power amplifier 100Aincludes a phase shifter 140A not including the capacitor 161 and aphase shifter 141A not including the inductor 171. The functions of thephase shifters 140A and 141A are similar to those of the phase shifters140 and 141 in the power amplifier 100. The power amplifier 100A may beformed on a single IC chip or multiple IC chips.

FIG. 9 is a diagram illustrating an example of a simulation result ofthe phase difference between the output of the carrier amplifier 111 andthe output of the peak amplifier 112 obtained in the power amplifier100A in FIG. 8. FIG. 9 also illustrates, as a comparative example, asimulation result obtained in a common Doherty amplifier including a λ/4transmission line on the output side of the carrier amplifier 111 inplace of the phase shifters 140A and 141A. In FIG. 9, the horizontalaxis represents the frequency (GHz), and the vertical axis representsthe phase difference (degrees). In the example illustrated in FIG. 9,the power amplifier 100A and the common Doherty amplifier are bothdesigned such that the phase difference is about 90 degrees when thefrequency of the signal RF_(IN) is about 1.9 GHz.

As illustrated in FIG. 9, in the common Doherty amplifier, the phasedifference varies substantially linearly in accordance with a change infrequency. That is, the rate of change of the phase difference isrelatively large near the frequency of 1.9 GHz. Meanwhile, in the poweramplifier 100A, the rate of change of the phase difference is relativelysmall near the frequency of about 1.9 GHz. This is because a change incharacteristics of the phase shifter 140A due to a change in frequencyis cancelled by a change in characteristics of the phase shifter 141Adue to a change in frequency. The simulation results in FIG. 9 thereforereveal that the power amplifier 100A is capable of better handling thesignal RF_(IN) having a broad band width than the common Dohertyamplifier.

It is also revealed from simulation results of the power addedefficiency (PAE) obtained in the common Doherty amplifier and the poweramplifier 100A that the power amplifier 100A is capable of handling thesignal RF_(IN) having a broad band width. FIGS. 10A and 10B arecharacteristics illustrating an example of simulation results, whereinthe horizontal axis represents the frequency (GHz) and the vertical axisrepresents the PAE (%). FIGS. 10A and 10B illustrate multiple simulationresults at different power levels of the signal RF_(IN).

As illustrated in FIG. 10A, in the common Doherty amplifier, theallowable PAE bandwidth is about 0.2 GHz, for example, when the centerfrequency is about 1.9 GHz. Meanwhile, as illustrated in FIG. 10B, inthe power amplifier 100A, the allowable PAE bandwidth is about 1.0 GHz,for example, when the center frequency is about 1.9 GHz. Thesesimulation results also reveal that the power amplifier 100A is capableof better handling the signal RF_(IN) having a broad band width than thecommon Doherty amplifier.

Although the simulation results illustrated in FIG. 9 and FIG. 10Brelate to the power amplifier 100A, it is obvious that similar effectsare also obtained in the power amplifier 100.

FIG. 11 is a diagram illustrating another configuration example of thepower amplifier. A power amplifier 100B includes a switch circuit 200 inaddition to the configuration of the power amplifier 100A. The sameconfigurations as those of the power amplifier 100A illustrated in FIG.8 are designated by the same reference numerals, and description thereofwill be omitted. The power amplifier 100B may be formed on a single ICchip or multiple IC chips.

The switch circuit 200 selects the path of the signal output from theinitial-stage amplifier 110 between the combining unit 142 and the 3 dBcoupler 130 in accordance with a power mode signal MODE that controls apower mode (output power) of the power amplifier 100B. Specifically, ina low power mode, for example, the switch circuit 200 switches thesignal path such that the signal output from the initial-stage amplifier110 is connected to the combining unit 142. Further, in a high powermode, for example, the switch circuit 200 selects the signal path suchthat the signal output from the initial-stage amplifier 110 is connectedto the 3 dB coupler 130.

The switch circuit 200 thus provided can skip power amplificationaccording to the power mode. The power amplifier 100B is designed suchthat the load-side impedance viewed from the capacitor 151 is R_(L) whenthe switch circuit 200 is connected to the 3 dB coupler 130.Accordingly, the power amplifier 100B is capable of suppressingimpedance fluctuations when the signal path is switched by the switchcircuit 200.

The present embodiment has been described above. The power amplifier100, 100A, or 100B according to the present embodiment is capable ofchanging the load impedance of the carrier amplifier 111 by turning onand off the operation of the peak amplifier 112 in accordance with thepower level of the signal RF_(IN), similarly to the common Dohertyamplifier. Accordingly, the power amplifier 100, 100A, or 100B accordingto the present embodiment is capable of performing high-efficiency poweramplification similarly to the common Doherty amplifier. Further, thepower amplifier 100, 100A, or 100B according to the present embodimentemploys the phase shifters 140 (140A) and 141 (141A), which include aninductor and a capacitor, respectively, in place of the λ/4 transmissionline of the common Doherty amplifier. Accordingly, the power amplifier100, 100A, or 100B according to the present embodiment is capable ofrealizing a reduction in size, as compared with the common Dohertyamplifier.

Further, in the power amplifier 100A or 100B according to the presentembodiment, the capacitor 161 of the phase shifter 140 and the inductor171 of the phase shifter 141 are omitted. It is thereby possible tofurther reduce the circuit size.

Further, in the power amplifier 100, 100A, or 100B according to thepresent embodiment, the 3 dB coupler 130 is employed as a power splitterthat splits signals to the carrier amplifier 111 and the peak amplifier112. The 3 dB coupler 130 has a small dimension and is formable on achip, and thus is capable of reducing the circuit size of the poweramplifier 100, 100A, or 100B.

Any given power splitter other than the 3 dB coupler 130 may also beemployed. For example, a combination of a Wilkinson divider and a phaseshifter or a branch-line(hybrid) may be employed as the power splitter.

Further, the power amplifier 100B according to the present embodiment iscapable of causing the signal output from the initial-stage amplifier110 to be input to the combining unit 142 or the 3 dB coupler 130 basedon the power mode signal. Accordingly, it is possible to perform poweramplification according to the power mode.

Further, it is possible to configure the power amplifier 100, 100A, or100B according to the present embodiment on a single IC chip.

While embodiments of the disclosure have been described above, it is tobe understood that the present embodiment is for facilitatingunderstanding of the present disclosure and not for limitinginterpretation of the present disclosure. It is also to be understoodthat variations, modifications, and improvements will be apparent tothose skilled in the art without necessarily departing from the scopeand spirit of the disclosure, and that the present disclosure includesequivalents thereof. The scope of the disclosure, therefore, is to bedetermined solely by the following claims.

What is claimed is:
 1. A power amplifier comprising: a power splitterthat splits a first signal into a second signal and a third signaldelayed from the second signal by about 90 degrees; a first amplifierthat outputs a fourth signal by amplifying the second signal when apower level of the first signal equals or exceeds a first level; asecond amplifier that outputs a fifth signal by amplifying the thirdsignal when the power level of the first signal equals or exceeds asecond level higher than the first level; a first phase shifter thatreceives an input of the fourth signal and outputs a sixth signaldelayed from the fourth signal by about 45 degrees; a second phaseshifter that receives an input of the fifth signal and outputs a seventhsignal advanced from the fifth signal by about 45 degrees; and acombining unit that outputs an amplified signal of the first signal bycombining the sixth signal and the seventh signal.
 2. The poweramplifier according to claim 1, wherein the first phase shifter includesa first inductor connected in series between the first amplifier and thecombining unit, and wherein the second phase shifter includes a firstcapacitor connected in series between the second amplifier and thecombining unit.
 3. The power amplifier according to claim 2, wherein thefirst phase shifter further includes a second capacitor having one endelectrically connected to the combining unit and an other end grounded,and wherein the second phase shifter further includes a second inductorhaving one end electrically connected to the combining unit and an otherend grounded.
 4. The power amplifier according to claim 1, wherein thepower splitter includes a coupled-line 3 dB coupler.
 5. The poweramplifier according to claim 1, further comprising a third amplifierthat outputs the first signal by amplifying an input signal.
 6. Thepower amplifier according to claim 5, further comprising a switch thatconnects the first signal to the power splitter or the combining unitbased on a power mode signal that controls output power.
 7. The poweramplifier according to claim 1, wherein the power splitter, the firstamplifier, the second amplifier, the first phase shifter, the secondphase shifter, and the combining unit are provided on a single IC chip.8. The power amplifier according to claim 2, wherein the power splitterincludes a coupled-line 3 dB coupler.
 9. The power amplifier accordingto claim 3, wherein the power splitter includes a coupled-line 3 dBcoupler.
 10. The power amplifier according to claim 2, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 11. The power amplifier according to claim 3, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 12. The power amplifier according to claim 4, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 13. The power amplifier according to claim 2, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 14. The power amplifier according to claim 3, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 15. The power amplifier according to claim 4, furthercomprising a third amplifier that outputs the first signal by amplifyingan input signal.
 16. The power amplifier according to claim 1, whereinthe power splitter, the first amplifier, the second amplifier, the firstphase shifter, the second phase shifter, and the combining unit areprovided on a single IC chip.
 17. The power amplifier according to claim2, wherein the power splitter, the first amplifier, the secondamplifier, the first phase shifter, the second phase shifter, and thecombining unit are provided on a single IC chip.
 18. The power amplifieraccording to claim 3, wherein the power splitter, the first amplifier,the second amplifier, the first phase shifter, the second phase shifter,and the combining unit are provided on a single IC chip.
 19. The poweramplifier according to claim 3, wherein the power splitter, the firstamplifier, the second amplifier, the first phase shifter, the secondphase shifter, and the combining unit are provided on a single IC chip.20. The power amplifier according to claim 4, wherein the powersplitter, the first amplifier, the second amplifier, the first phaseshifter, the second phase shifter, and the combining unit are providedon a single IC chip.
 21. The power amplifier according to claim 5,wherein the power splitter, the first amplifier, the second amplifier,the first phase shifter, the second phase shifter, and the combiningunit are provided on a single IC chip.
 22. The power amplifier accordingto claim 6, wherein the power splitter, the first amplifier, the secondamplifier, the first phase shifter, the second phase shifter, and thecombining unit are provided on a single IC chip.